Umaima is 5 times as old as William and is also 20 years older than William. How old is William?
Answer: We can use the given information to write down two equations that describe the ages of Umaima and William. Let Umaima's current age be $u$ and William's current age be $w$ $u = 5w$ $u = w + 20$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $w$ , and both of our equations have $u$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 =$ $5w$ $-$ $ (w + 20)$ which combines the information about $w$ from both of our original equations. Solving for $w$ , we get: $4 w = 20$ $w = 5$.